The subject invention relates to a variable ratio drive system for a vehicle that utilizes a series of drive motors in combination with a single planetary gear box to provide driving input to an axle differential.
Electric drive motor systems for a vehicle drive axle assembly typically do not have the capability to efficiently control the complete range of torque and speed requirements of a wheel driven vehicle. Heavy duty vehicles, such as trucks and buses for example, require a wide range of torque and speeds to accommodate the often strenuous and diverse duty cycles to which these types of vehicles are subjected. Traditionally, in order to accommodate these torque and speed range requirements, either a complex transmission is required or a large capacity variable speed electric motor must be used as a power source. Either of these solutions is expensive. A further disadvantage is that this large capacity power source has to use a conventional axle gear differential to transfer the torque to driving wheels on the axle assembly, and the combination of a conventional differential and large capacity power source is difficult to install within the available packaging space.
One proposed solution has been to utilize independent motor drives at each wheel. This requires a separate power source and drive gear set at each wheel. This configuration eliminates the need for a conventional differential, however, the use of a motor and drive gears for each powered wheel significantly increases system costs.
Thus, there is a need for a variable ratio drive motor configuration for an axle assembly that provides for a wide range of operational torques and speeds. This motor configuration should be easily incorporated into an axle having a differential assembly as well as overcoming the other above-mentioned deficiencies in the prior art.